JPH0995795A - Zinc-nickel alloy electroplated steel sheet excellent in plating adhesion and chemical convertibility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a Zn-Ni alloy electroplated steel sheet excellent in chemical convertibility. SOLUTION: This Zn-Ni alloy electroplated steel sheet excellent in plating adhesion and chemical convertibility is the one in which at least one side of a steel sheet is applied with a plating layer contg., by weight, 8 to 18% Ni, 5 to 100ppm Sn or In or both of Sn and In by 5 to 100ppm in total. Furthermore, at the time of applying Zn-Ni alloy electroplating to the steel sheet, it is executed in such a manner that the concn. of Ni<2+> in the plating bath is regulated to 10 to 50g/l, the concn. of Zn<2+> is regulated to 50 to 200g/l, the mollar concn. ratio of Ni<2+> /Zn<2+> is regulated to 0.05 to 0.4, furthermore, Sn or In is allowed to contain by 0.05 to 5ppm or both of Sn and In by 0.05 to 5ppm in total, the pH in the plating bath is regulated to 3.0 to 5.5, and the bath temp. is regulated to <=70 deg.C. Thus, the objective Zn-Ni alloy electroplated steel sheet excellent in plating adhesion and chemical convertibility can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Zn-Ni alloy electroplated steel sheet used for automobiles, home appliances, building materials and the like, and in particular, Zn-for automobiles having excellent chemical conversion treatability as compared with conventional materials. Ni-based alloy electroplated steel sheet.

[0002]

2. Description of the Related Art When a plated steel sheet is used as a steel sheet for automobiles, for example, it is subjected to chemical conversion treatment such as phosphate treatment. It has a great influence on the overall performance of the coating film formed. On the other hand, various kinds of anticorrosive steel sheets for automobiles have been developed so far, but only a few kinds are industrially used in the automobile industry. Among them, the demand for Zn-Ni alloy electroplated steel sheets as high corrosion-resistant surface-treated steel sheets is ever increasing.

This is because Zn-Ni alloy electroplating is easier to control the coating amount and is easier to make a thinner weight than hot-dip galvanizing or alloying hot-dip galvanizing.
This is because the life of the tip can be extended by welding, and the bare corrosion resistance is superior to that of hot-dip galvanizing with heavy weight. Examples of the method for producing a Zn-Ni alloy electroplated steel sheet include JP-A-55-131193, JP-A-55-152194, and JP-A-57-164999.

All of these are focused on the technique for stably producing a Zn-Ni plated steel sheet according to the regulation of the plating bath composition and the regulation of the plating conditions. However, Zn-Ni alloy electroplated steel sheets obtained by these methods have been found to cause chemical conversion treatment defects such as unevenness and unevenness in the coating line in the automobile manufacturing process, and therefore various preventive measures have been taken. A review was made.

As a result, for the purpose of improving the chemical conversion processability,
A surface layer control technique for a Zn-Ni alloy electroplated steel sheet has been disclosed. As a method for disclosing a surface layer control technique for a Zn-Ni alloy electroplated steel sheet, JP-A-58-45382 and JP-A-62-45382 are disclosed.
294197, JP 63-26396, JP 63-93
879, JP 1-255676, JP 1-1984
98, JP-A-2-259095, JP-A-2-277796
And the like.

Japanese Unexamined Patent Publication (Kokai) No. 58-45382 discloses a Zn-Ni alloy electroplated steel sheet, which is characterized by subjecting it to a pretreatment in which an acidic liquid having a pH of 2.5 or less is brought into contact with Zn, which has excellent chemical conversion treatment properties. −
A method for manufacturing a Ni-plated steel sheet is disclosed. JP 62-29
Japanese Patent No. 4197 discloses a method of activating the plating surface by treating the outer layer of Zn-Ni plating in a plating solution or an acid solution.

In Japanese Patent Laid-Open No. 63-26396, Zn-
A method is disclosed in which a part of the Ni-based alloy electroplating layer is dissolved with a mineral acid, an organic acid, or the like, or reverse electrolysis is performed with the steel sheet as the anode side. JP 63-93879 A
Since the surface layer of Zn-Ni alloy plating is rich in zinc, excellent chemical conversion treatment was achieved by etching the surface layer of the plating with a weakly acidic solution in the range of 0.01 to 1 g / m ² .
A technique for obtaining a Zn-Ni plated steel sheet is disclosed. As a weakly acidic solution in this case, a Zn-Ni plating solution, diluted sulfuric acid or diluted hydrochloric acid is disclosed.

Japanese Unexamined Patent Publication No. 1-255676 discloses a steel sheet containing Zn--
After continuous electroplating of Ni alloy, the plating film is treated with a strong alkaline solution of pH 11 or more such as sodium orthosilicate,
A method for improving chemical conversion treatability by forcibly dissolving and removing an oxide film formed unevenly on the plating surface is disclosed. Japanese Patent Laid-Open No. 1-198498 discloses Zn-
A method of improving chemical conversion treatability by depositing a specific amount of Ni by electroless plating after performing Ni-based alloy plating is disclosed.

Japanese Unexamined Patent Application Publication No. 2-259095 discloses that a plating bath
Disclosed is a technique for obtaining plating with excellent chemical conversion treatability by controlling the Ni ²⁺ and Zn ²⁺ concentrations and performing electroplating in a plating bath containing a Sr compound or Ba compound and a trace amount of Pb. . Japanese Patent Laid-Open No. 2-277796 discloses a technique for obtaining a Zn-Ni plated steel sheet having excellent chemical conversion treatability by performing Zn-Ni plating in a plating bath in which the amount of Pb dissolved is specified.

Japanese Patent Publication No. 6-80194 discloses that a Sr compound and / or a Ba compound is added to the Zn-Ni alloy electroplating layer.
And / or 10 to 1000ppm as Ba, 50 to 200ppm Pb
Disclosed is a Zn-Ni-based electroplated steel sheet having excellent chemical conversion treatability. The method for manufacturing the conventional Zn-Ni alloy electroplated steel sheet has been described above, but the conventional technology has the following problems.

The above-mentioned JP-A-58-45382 and JP-A-62.
-294197, JP 63-26396, JP 63-9
3879, JP-A-1-255676, and JP-A-1
The method described in Japanese Patent Publication No. 198498 improves the chemical conversion treatability by removing the zinc-rich layer formed on the plating surface layer by using an acidic solution or an alkaline solution and homogenizing the plating surface layer. The purpose is to let.

However, all the methods disclosed in these publications are based on the premise that the zinc-rich layer is completely removed by using a post-treatment liquid, which leads to an increase in the plating unit consumption and The partial post-dip treatment may rather make the plating surface non-uniform. For example, in the post-dip treatment using a plating solution, the zinc-rich layer on the plating surface is preferentially dissolved and nickel is displaced and deposited at the same time, but as a result, a nickel-rich layer is formed in the process. The unevenness of the plated surface may be amplified.

Further, when the zinc-rich layer is removed by using an acidic solution or an alkaline solution, the above-mentioned phenomenon does not occur, but since the internal stress of the plating layer is relaxed, countless cracks are formed in the plating layer. appear. As a result, the plating adhesion is drastically reduced. From the above, although the method of completely removing the zinc-rich layer has advantages, it also has the above-mentioned drawbacks.

The techniques disclosed in the above-mentioned JP-A-2-259095 and JP-A-2-277796 disclose a Zn--Ni alloy alloy excellent in chemical conversion treatability by defining the components in the plating bath. It is an attempt to obtain plating. The common feature of these technologies is that the plating bath contains a specified amount of lead ions. However, lead ions are a metal that reduces plating adhesion, and conventionally they are removed. It is clear that this is not always a satisfactory method in view of the fact that various studies have been carried out.

The fatal deficiency of the above technique is that the main purpose is to simply remove the zinc-rich layer on the surface of the plating, and the effect of the amount of zinc-rich layer on the chemical conversion treatability is completely taken into consideration. That is not done. That is, even when Zn-Ni alloy electroplating was performed using the above technique, not all were excellent in chemical conversion treatability. In particular, the chemical conversion treatability is often determined by the degreasing conditions that are the previous step,
At manufacturing sites where the degreasing liquid is rarely renewed, deterioration of the degreasing liquid was likely to cause chemical conversion treatment failure.

The method disclosed in the above Japanese Patent Publication No. 6-80194 is such that Sr, Ba,
By containing Pb and the like, the chemical conversion treatability is improved, and the method is different from the above technique.
However, the drawback of this technique is that Pb is contained in the plating solution,
Moreover, it was also deposited in the plating layer. That is, it is known that Pb is a metal that significantly reduces the adhesion of the coating film after coating, and it is not preferable to use Pb only to improve the chemical conversion treatability from the viewpoint of maintaining the properties of the plated steel sheet. .

[0017]

SUMMARY OF THE INVENTION The present invention provides a Zn-Ni alloy electroplated steel sheet having excellent chemical conversion treatability and a method for producing the same, which solves all the problems of the prior art.

[0018]

The first invention is to reduce the number of steel plates.
If at least one surface has a Ni content of 8-18 wt%, Sn and
And / or In containing a plating layer containing 5 to 100 ppm in total
Plating adhesion and chemical conversion treatability characterized by having
Excellent Zn-Ni alloy electroplated steel sheet. Second departure
Ming is, when performing Zn-Ni alloy electroplating on steel sheets,
Ni in the bath ²⁺Concentration 10 ~ 50g / l, Zn²⁺50-200g concentration
/ l, Ni²⁺/ Zn²⁺The molar concentration ratio of 0.05 to 0.4, and
Contain 0.05 to 5 ppm of Sn and / or In in total
Therefore, the plating bath pH should be 3.0 to 5.5 and the bath temperature should be 70 ° C or less.
Plating adhesion and conversion characterized by vapor plating
Manufacturing method of Zn-Ni alloy electroplated steel sheet with excellent processability
Is the law.

In the present invention, 1 ppm means 1 × 10 ⁻⁴ wt%.

[0020]

[Function] The Zn-Ni alloy electroplated steel sheet targeted by the present invention means Zn-Ni, Zn-Ni-Cr, Zn-Ni-Co, Zn-Ni-Fe, Zn-N.
It also includes alloy electroplated steel sheets having alloy plating such as i-Fe-Cr, and those containing oxide fine particles such as SiO ₂ , TiO ₂ , and Al ₂ O ₃ in these alloy plating.

In the plated steel sheet of the present invention, the Ni content of the plated layer is 8 to 18 in any of these platings.
It should be wt%, preferably 10-15 wt%. 8 wt%
If it is less than 18, the corrosion resistance of the plating cannot be sufficiently secured.
This is because if it exceeds wt%, the deterioration of plating adhesion becomes a problem. In the present invention, in addition to Zn and Ni, Sn and / or
Alternatively, it is necessary to contain In in the plating layer.

When Sn or In is contained alone, the content of Sn or In in the plating layer is 5 to 5.
When it contains both Sn and In, the total amount thereof should be 5 to 100 ppm. If it is less than 5 ppm, the effect of improving the chemical conversion treatment property is not sufficient, and surface defects such as unevenness partially occur on the surface of the steel sheet during the chemical conversion treatment, which is not preferable. On the contrary, if it exceeds 100 ppm, the excellent corrosion resistance of the Zn-Ni alloy plating may be deteriorated, which is not preferable.

Further, it is more preferable to add both of Sn and In than to add them in a large amount, because the chemical conversion treatability and the adhesion are further improved. The coating amount is not particularly limited, but if the purpose is to improve corrosion resistance, it is preferably 10 g / m ² or more per one side of the steel plate, and more preferably 20 g / m ^2.
The range of -40 g / m ² is preferred. Next, the manufacturing method of the present invention will be described.

The Ni ²⁺ concentration in the plating bath should be 10 to 50 g / l. If it is less than 10 g / l, the diffusion of metal ions to the cathode side is rate-determining, the current efficiency is reduced, and uniform alloy plating cannot be obtained. When it exceeds 50 g / l, although it depends on the concentration of other metal ions, precipitation of Ni is likely to occur and stable operation becomes difficult, which is not preferable. The Zn ²⁺ concentration in the plating bath should be 50 to 200 g / l. If it is less than 50 g / l, non-uniform plating may occur due to a decrease in current efficiency, and if it exceeds 200 g / l, Zn precipitation is likely to occur, which is not preferable.

The molar concentration ratio of Ni ²⁺ / Zn ²⁺ must be 0.05 to 0.4. That is, if it is less than 0.05, it is difficult to obtain an alloy plating having a Ni content of 8 wt% or more even if the plating conditions such as the current density, the plating solution flow rate and the line speed are adjusted within the normal operating range. Ni content exceeds
It is not preferable because it exceeds 18 wt%. In the present invention,
In addition to Zn ²⁺ and Ni ^{2+ in} the plating bath, Sn and / or
It is necessary to contain In.

When any one of Sn and In is contained in the plating layer, the content of Sn or In in the plating solution is 0.05 to 5 ppm. When both Sn and In are contained in the plating layer, the total content of Sn and In in the plating solution is set to 0.05 to 5 ppm as described above. If it is less than 0.05 ppm, it is difficult to secure the predetermined precipitation amounts of those elements in the Zn-Ni alloy plating layer, and it is difficult to improve the chemical conversion treatability. On the contrary, if it exceeds 5 ppm, the amount of eutectoid in the plating layer becomes excessive, which may reduce the corrosion resistance of the plating itself, which is not preferable.

The Sn and In contents in the plating solution are such that the total amount of metal and ions is within the above range. The pH of the plating bath is in the range of 3.0 to 5.5, preferably
A range of 3.5 to 5.0 is suitable. If it is less than 3.0, the amount of Sn and / or In codeposited in the plating layer may not reach a predetermined amount, and if it exceeds 5.5, only burnt plating can be obtained, which is not preferable.

The plating bath temperature is 70 ° C. or lower, preferably 35 to
It shall be in the range of 65 ℃. If the temperature exceeds 70 ° C, corrosion of the equipment is likely to occur and it is uneconomical. Further, when the plating bath temperature is lower than 35 ° C., it is difficult to control the Ni content to a predetermined amount, and it is difficult to operate at high current density. The plating bath is preferably a chloride bath from the viewpoint of the solubility of Sn and In, and in that case, a conduction aid such as NH ₄ Cl, KCl or NaCl can be used.

Regarding the current density and the plating solution flow rate in actual operation, conditions suitable for the line may be adopted. The current density is 40 to 150 A / dm ² , and the plating solution flow rate is 30 to 150 m.
/ min is a practical range. Examples of the supply of Sn and In include a method of electrolyzing a metal, a method of dissolving a metal with an acid such as hydrochloric acid or sulfuric acid, a method of directly supplying a powder of a sulfuric acid compound, a carbonic acid compound, a chloride or the like to a bath, It is not necessarily limited to these.

[0030]

[Example] In the electroplating line, the plating bath composition,
The electrolysis conditions were set so as to have the composition and conditions shown in Table 2,
Various plated steel sheets having different amounts of zinc-rich layers were manufactured, the obtained plated steel sheets were cut into 300 × 300 mm pieces, and then subjected to the following chemical conversion treatment test and plating adhesion test. The main constituents of the plating bath are zinc chloride, nickel chloride and potassium chloride.

[Chemical conversion treatment test] In the chemical conversion treatment test, a PB-L3020 system manufactured by Nippon Parkerizing Co., Ltd. was used,
Zinc phosphate treatment was performed. The outline of the PB-L3020 system is the recommended conditions of the manufacturer [Nihon Parkerizing Co., Ltd.] shown in Table 1. Note that the pH of the degreasing liquid should be adjusted in consideration of deterioration (decrease in pH) of the degreasing liquid during process production.
= 10 (new bath: pH = 12).

[0032]

[Table 1]

The chemical conversion treatability was evaluated visually. The criteria are as follows. ⊚: When the chemical conversion coating has no flow pattern or black streaks. ◯: When a flow pattern or black streaks are partially generated in the chemical conversion treatment film (less than 5% of the steel plate surface area). Δ: When a flow pattern or black streaks are partially generated on the chemical conversion coating (5% or more of the surface area of the steel sheet).

X: When a flow pattern or black streaks are formed on the entire surface of the chemical conversion treatment film. Further, the chemical conversion coating is subjected to X-ray diffraction, and the surface ratio [I (02
0) / I (151, 241, 311)] was investigated. Note that I
(020) is the peak intensity of the (020) plane, I (151, 241, 3
11) indicates the peak intensity of the (151, 241, 311) plane.
It is known that as the surface ratio increases, the secondary resistance to water resistance decreases, so the surface ratio of the crystal of the chemical conversion coating was used as the acceptance criterion.

[Plating Adhesion Test] The obtained plated steel sheet was further cut into 40 mm × 40 mm, cellophane tape was attached, and the test piece was bent 90 degrees so that the surface on which the cellophane tape was attached was on the inside, It was folded back to form the original flat plate, the cellophane tape was peeled off, and the amount of Zn (count value) attached to the cellophane tape was determined by fluorescent X-ray analysis.

The judgment criteria are as follows. ◎: 0 to 200 CPS (CPS: Counts Per Second) ○: 201 to 800 CPS △: 801 to 1500 CPS ×: 1501 CPS or more The test results obtained are shown in Table 2 together with the plating bath composition and electrolysis conditions. .

[0037]

[Table 2]

[0038]

[Table 3]

From Table 2, it can be seen that the present invention provides a plated steel sheet having excellent chemical conversion treatability even when the degreasing liquid in the chemical conversion treatment step deteriorates (pH decreases).

[0040]

EFFECTS OF THE INVENTION The present invention provides a Zn—Ni alloy electroplated steel sheet which is excellent in chemical conversion treatability and is not easily affected by fluctuations in operation in the chemical conversion treatment step, and its industrial significance is great.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomokatsu Katagiri 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture, Kawasaki Steel Corporation Technical Research Institute (72) Inventor Shuichi Asahina 1 Kawasaki-cho, Chuo-ku, Chiba-shi (72) Inventor Kazuo Mochizuki, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd.

Claims (2)

[Claims] 1. A steel sheet having a Ni content of 8 to 18 wt% and a total amount of Sn and / or In of 5 to 10 on at least one surface of the steel sheet.
A Zn-Ni-based alloy electroplated steel sheet having excellent plating adhesion and chemical conversion treatability, which has a plating layer containing 0 ppm. 2. When performing Zn-Ni alloy electroplating on a steel sheet, the Ni ²⁺ concentration in the plating bath is 10 to 50 g / l and the Zn ²⁺ concentration is
50 to 200g / l, Ni ²⁺ / Zn ²⁺ molar concentration ratio is 0.05 to 0.4, and the total amount of Sn and / or In is 0.05 to 5ppm
A method for producing a Zn-Ni-based alloy electroplated steel sheet having excellent plating adhesion and chemical conversion treatment, characterized in that electroplating is carried out at a plating bath pH of 3.0 to 5.5 and a bath temperature of 70 ° C or less.